Sean O'Brien powers over to score a try against the Melbourne Rebels. Photograph: David Davies/PA

PHYSICAL MOMENTUM

The dirt-trackers have had their last outing, confined to tackle-bag duty for the rest of the British & Irish Lions tour unless, or should that be until, more injuries strike. They stepped off the stage in style, running away from the Melbourne Rebels in a romp that highlighted how rugby union has changed in the past 20 years.

All the Super 15 teams the Lions have played here have been below strength, shorn of their current national squad players, and what was exposed in Melbourne again was the superior strength and conditioning of the tourists which rendered the Rebels' resolve redundant.

Twenty years ago, when the Lions were in New Zealand, their midweek side fell away, not only losing to Hawke's Bay and a Waikato side that included Warren Gatland in its front row, but being blown away physically. What the last couple of Lions tours have shown, and New Zealand in four years' time will be interesting, is that Test teams are so well conditioned and physical that there is a significant gap even between top provincial/club players and ones in the Test arena.

The Lions lost to the Brumbies last week when they fielded three backs who had only just joined the tour. That unfamiliarity told and, together with the morale-wobbling factor of the players in the starting line-up realising that their chances of making the Test XV were worse than those of an Australia cricket coach seeing out his contract, gave the home side an in.

The Rebels got stuck in and their tackling was initially ferocious, but their lack of possession meant they played for long periods on the back foot and they lacked the power of the Lions. Back in the day, when rugby union tended to move from one set piece to the next, differences in conditioning were nowhere near as pronounced.

The disparity raises the question about the viability of warm-up matches. The result is not often in doubt and the contest in Melbourne this week came to be about whether the Rebels could score a try, not whether they could win. The public address system pointed out that a record crowd had been attracted to a rugby union match at the ground, but the majority of the spectators were clad in red.

The warm-up matches allow a tour to develop a momentum, and without them the Lions would not exist because there is no practical way a team from four countries could arrive in Australia, South Africa and New Zealand and go straight into the first Test: it was demanding enough for the Wallabies to start the series not having had a warm-up international.

The tour has also shown the advances in conditioning in the northern hemisphere. When the game turned professional, Wales, Ireland and Scotland in particular struggled to compete physically with the leading southern hemisphere sides. Wales toured Australia in 1996 and were knocked about.

The Lions have the advantage in size here, led by players from Wales and Ireland. Sean O'Brien may not have been in the 23 for the first Test, but he is a player Australians admire for his power and stamina: they have not forgotten the role he played in the 2011 World Cup victory over the Wallabies in Auckland.

"The Lions have an embarrassment of riches in their back row," said Matt Cockbain, a Wallaby flanker when the Lions were here in 2001 who is now on the Rebels' coaching team. "I rate the trip that started last week: I was standing next to Tom Croft after our game and, while he is wiry, he is a big man.

"Jamie Heaslip does a job at No8 and the captain is at seven. O'Brien is unlucky: he is a player I really rate and then there are Toby Faletau and Dan Lydiate. I think the Lions will stick to last week's three, but Warren Gatland has a difficult job in deciding the combination.

"I think the Lions have been outstanding. They had a blip against the Brumbies when they maybe had a few players brooding about not being in the Test side, but they were pretty much dominant in the other matches up to the first Test. It is a long way back for the Wallabies: we were one down in 2001, but we were the World Cup holders then and we had a number of players who would have made a World XV. You cannot say that about the current team."

When the World Cup draw was made last year and Australia found themselves in a group with the hosts, England, and Wales, there was almost a default assumption that it was a battle between the two home unions for the second quarter-final position.

The Wallabies have won the two previous World Cups held in Britain, in 1991 and 1999, but they have a way to go to make it a hat-trick. England are developing strength in depth and Wales, Six Nations champions in 2012 and this year, will probably have the most experienced squad in the 2015 tournament.

All of their current squad could, given a few vigorous rubdowns, be in the set-up in two years, although the prop Gethin Jenkins, who has become susceptible to calf strains, and scrum-half Mike Phillips may find it a stretch. Wales look vulnerable only at half-back and in two years the likes of Leigh Halfpenny, Jonathan Davies, George North, Jamie Roberts, Alun Wyn Jones and the back row trio will be in their pomp.

Australia have some stand-out backs, most notably Will Genia and Israel Folau, but at forward, with David Pocock injured, they have no major characters, nobody in their position who stands out. The game here is struggling financially, which has forced a revamp of the academy system, and where the green and gold used to lead, now they follow.